> On Jul 18, 2024, at 19:20, Muchun Song <muchun.song@xxxxxxxxx> wrote: > > > >> On Jul 18, 2024, at 18:30, Vlastimil Babka <vbabka@xxxxxxx> wrote: >> >> On 7/18/24 10:36 AM, Muchun Song wrote: >>> The mem_cgroup_from_slab_obj() is supposed to be called under rcu >>> lock or cgroup_mutex or others which could prevent returned memcg >>> from being freed. Fix it by adding missing rcu read lock. >> >> Was the UAF ever observed, or is this due to code review? > > Just code review. > > Thanks. > >> Should there be some lockdep_assert somwhere? >> > > It’s a good option to improve this. Maybe mem_cgroup_from_slab_obj() is a good place. I added it to obj_cgroup_memcg() [1]. And CC memory cgroup maintainers to this thread. [1] https://lore.kernel.org/linux-mm/20859F67-A80C-4FD0-990C-40C70905E55B@xxxxxxxxx/T/ > >>> Fixes: 0a97c01cd20bb ("list_lru: allow explicit memcg and NUMA node selection) >>> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx> >>> --- >>> mm/list_lru.c | 24 ++++++++++++++++++------ >>> 1 file changed, 18 insertions(+), 6 deletions(-) >>> >>> diff --git a/mm/list_lru.c b/mm/list_lru.c >>> index 3fd64736bc458..225da0778a3be 100644 >>> --- a/mm/list_lru.c >>> +++ b/mm/list_lru.c >>> @@ -85,6 +85,7 @@ list_lru_from_memcg_idx(struct list_lru *lru, int nid, int idx) >>> } >>> #endif /* CONFIG_MEMCG_KMEM */ >>> >>> +/* The caller must ensure the memcg lifetime. */ >>> bool list_lru_add(struct list_lru *lru, struct list_head *item, int nid, >>> struct mem_cgroup *memcg) >>> { >>> @@ -109,14 +110,20 @@ EXPORT_SYMBOL_GPL(list_lru_add); >>> >>> bool list_lru_add_obj(struct list_lru *lru, struct list_head *item) >>> { >>> + bool ret; >>> int nid = page_to_nid(virt_to_page(item)); >>> - struct mem_cgroup *memcg = list_lru_memcg_aware(lru) ? >>> - mem_cgroup_from_slab_obj(item) : NULL; >>> + struct mem_cgroup *memcg; >>> >>> - return list_lru_add(lru, item, nid, memcg); >>> + rcu_read_lock(); >>> + memcg = list_lru_memcg_aware(lru) ? mem_cgroup_from_slab_obj(item) : NULL; >>> + ret = list_lru_add(lru, item, nid, memcg); >>> + rcu_read_unlock(); >>> + >>> + return ret; >>> } >>> EXPORT_SYMBOL_GPL(list_lru_add_obj); >>> >>> +/* The caller must ensure the memcg lifetime. */ >>> bool list_lru_del(struct list_lru *lru, struct list_head *item, int nid, >>> struct mem_cgroup *memcg) >>> { >>> @@ -139,11 +146,16 @@ EXPORT_SYMBOL_GPL(list_lru_del); >>> >>> bool list_lru_del_obj(struct list_lru *lru, struct list_head *item) >>> { >>> + bool ret; >>> int nid = page_to_nid(virt_to_page(item)); >>> - struct mem_cgroup *memcg = list_lru_memcg_aware(lru) ? >>> - mem_cgroup_from_slab_obj(item) : NULL; >>> + struct mem_cgroup *memcg; >>> >>> - return list_lru_del(lru, item, nid, memcg); >>> + rcu_read_lock(); >>> + memcg = list_lru_memcg_aware(lru) ? mem_cgroup_from_slab_obj(item) : NULL; >>> + ret = list_lru_del(lru, item, nid, memcg); >>> + rcu_read_unlock(); >>> + >>> + return ret; >>> } >>> EXPORT_SYMBOL_GPL(list_lru_del_obj); >>> >>
